In relation to the background of the invention it should be noted that isolation amplifiers are used, among other things, for the acquisition and conditioning of analog measurement signals with dangerous potentials with regard to currents induced on contact with the human body, and in particular of measurement signals with high-voltage potential. Isolation amplifiers therefore convert the measurement signal, possibly via conversion into auxiliary variables, in a galvanically isolated manner into output signals representing the measurement signal in analog or digital form, wherein the output signals are usually at close to earth potential and are harmless if touched.
In the following descriptions, the term “high voltage” or “high-voltage potential” comprises all voltages and potentials that are dangerous when touched, the term “low voltage” or “low-voltage potential” covers all voltages and potentials that are not dangerous when touched. In the following descriptions therefore, the term “high-voltage isolation amplifier” covers all isolation amplifiers which are suitable for the measurement signal transmission and for the conversion of measurement signals that are dangerous when touched into output signals that are harmless when touched.
In order to enable a galvanic isolation between the high-voltage and low-voltage side, an end-to-end isolation barrier is required, which is implemented in known ways by potential-isolating coupling sections for transmitting a signal representing the measurement signal and, if appropriate, auxiliary variables and electrical energy.
Isolation amplifiers according to the prior art are often designed according to the structure shown in FIG. 3. Three different types of electrical switching circuits can be distinguished, namely an input circuit 1, an output circuit 2 and a primary current supply circuit 41, which are isolated from each other by galvanically isolating coupling sections 3, 42, 43. Each circuit 1, 2, 41 has at least one terminal in the form of the input 6, the output 15 and the primary current supply terminal 44, which is generally conductively connected to the associated electrical circuit. The potentials at which the circuits 1, 2, 41 lie are determined by the potentials of the external signal circuits or external power circuits connected to the associated terminals 6, 15 and 44. The terminals 6, 15 and 44 are also referred to as ports, and therefore FIG. 3 specifies an isolation amplifier with three galvanically separated ports. In detail, the structure shows an input circuit 1 with at least the input 6 for measurement signals with input circuit potential, wherein in the input circuit 1, a coupling section signal representing the measurement signal is generated and this coupling section signal is transmitted via a galvanically isolating coupling section 3 to the output circuit 2 at output circuit potential. In the output circuit 2, the coupling section signal is converted back into a signal which represents the measurement signal, and which can be output via the at least one output 15. The electrical energy required for the operation of all electronic elements in the input circuit 1, output circuit 2 and the coupling section 3 is extracted from the at least one primary power supply terminal 44. The primary power supply terminal 44, which is at primary power circuit potential, delivers the electrical energy to a primary power supply circuit 41, which contains suitable electronic means to deliver electrical energy via the galvanically isolating coupling sections 42 and 43, in each case matching the secondary power supply circuits 45 and 46 of the input and output circuit 1 and 2.
In accordance with the prior art, isolation amplifier structures are known in which the number of coupling sections is reduced. For example, this can be carried out by dispensing with a galvanic isolation between the primary power supply circuit 41 and output circuit 2. The coupling section 43 is then omitted and a direct galvanically conducting connection exists between these circuits instead. Such an isolation amplifier then has only two ports that are galvanically separated from each other.
Another possibility for reducing coupling sections is obtained as follows: the coupling section 42 can be omitted if via a suitable coupling section 3, for example a transformer, both electrical energy from the output circuit 2 to the input circuit 1 as well as a coupling section signal representing the measurement signal are transmitted via the same coupling section 3 from the input 1 to the output circuit 2, represented for example by the electrical current amplitude. The elimination of the coupling section 42 in this case does not reduce the number of ports that are galvanically isolated from each other.
In addition to the coupling sections mentioned, an end-to-end isolation barrier is implemented in general by an encapsulation which is as complete as possible, for example by means of an isolation amplifier housing suitable for this purpose and/or possibly by potting an entire isolation amplifier, or at least by potting all circuit sections that are galvanically connected to the high-voltage potential. Potting is used in particular when the measurement signals have particularly high voltages or potentials. In addition to a potting, other forms of insulation coatings are also possible, such as suitable paints, resins or molding-technology coatings and encapsulation methods.
A potential-isolating coupling section can work by inductive, capacitive, optical, electro-mechanical or electromagnetic coupling or a combination of these, depending on the type of coupling section chosen. Electromechanical coupling sections also include, for example, those which use the piezoelectric effect. The signal to be transmitted, or else the electrical energy to be transmitted, over the coupling section is converted into a signal which is designated generally in the following as a coupling section signal.
The coupling section signal thus includes the term “signal”, regardless of whether it is a signal which represents, for example, a measurement signal and/or a signal for transmission of electric energy. The coupling section signal is suitable for transmission over the respective type of galvanically isolating coupling section and, if applicable, for being converted back into such a signal, with which the desired further processing is possible. The conversion of a measurement signal into a coupling section signal and, if applicable, the back conversion of the coupling section signal into a subsequently processable signal representing the measurement signal, can be carried out e.g. by a modulator and demodulator. It goes without saying that for coupling sections which are (also) intended for the transmission of electrical energy, transformers in particular are preferably used. In contrast, commercially available so-called optocouplers are rather unsuitable for the transmission of electrical energy. Accordingly, the electrical energy of a primary power supply circuit can be converted into a suitable signal using well-known power supply topologies and then transmitted in a galvanically isolated manner, for example, with a coupling section implemented as a transformer and then, for example, by means of a rectifier circuit converted into a DC signal for supplying power to the input circuit and the output circuit.
The following explanations of possible coupling section signals, which are also able to represent measurement signals, apply regardless of the temporal waveform and the polarity of an input signal (measurement signal) present at the input of the isolation amplifier. A coupling section signal can be an alternating signal, which is particularly suitable for capacitive and inductive coupling sections. But it can also be an analog-based DC signal (DC voltage or DC current), which can be transmitted, for example, with optical coupling sections. An alternating signal can be an alternating voltage or an alternating current or else a pulsed DC voltage or a pulsed direct current.
Alternating signals can use analog forms of representation and/or contain digital encodings, they can be pulse-, pulse-width-, frequency-, phase-, amplitude- and digitally modulated signals or combinations thereof, wherein other modulation types are possible.
In the case of so-called single-range devices, high-voltage-side elements for device conditioning, such as for setting the gain, offset and frequency bandwidth are calibrated prior to encapsulation, for example, encapsulation by potting. A change in the operation or a subsequent calibration of a fully encapsulated device is then no longer possible without weakening the isolation or, in some cases, even without damage to the isolation. A weakening of the isolation may be simply opening a lid covering the input elements, or the removal of a cover or a suitable housing part of a correspondingly shaped housing for covering such input elements. This is particularly the case for multi-range devices in accordance with the prior art. Input elements can be both operating elements as well as a calibration/configuration/programming interface or any other interface for influencing isolation amplifier functions or isolation amplifier parameters.
To enable a high-voltage-side adjustability and operability of the isolation amplifier, regions of the input circuit can be excluded from encapsulation, e.g. in order to keep mechanically operated controls free of potting compound.
This is the case, for example, in the high-voltage VariTrans® P 42000 belonging to the applicant, which represents the closest prior art                see www.knick-international.com/de/products/proline/high-voltagetransducers/varitrans-p-42000/index.html#-.        
In this prior art an input circuit is provided at high-voltage potential with an input for a measurement signal to be transmitted, an input circuit for providing a coupling section signal representing the measurement signal, and an input circuit-side control unit for controlling the input circuit. The measurement signal is transmitted as a coupling section signal in a potential-isolating manner via a galvanically isolating coupling section to an output circuit at low-voltage potential. The latter has an output circuit for generating an output signal representing the measurement signal from the transmitted coupling section signal, an output for the output signal and a low-voltage-side unit for driving the output circuit.
This known multi-range device measures and converts measurement voltages up to 3600 V DC, wherein its isolation is designed for working voltages in AC/DC up to this level. The measuring ranges of the device are selected using a rotary coding switch, which is located electrically on the high-voltage side of the isolation amplifier. Therefore, special design measures are necessary, such as an extension of the plastic shaft of the rotary coding switch, so that the control knob of the rotary coding switch is safe to the touch in the interests of protection against dangerous shock currents. A calibration of such an isolation amplifier at high input voltages is very time-consuming due to the configuration and calibration interface being arranged on the input side. This places high demands on the insulation of test and calibration devices.
Generally speaking therefore, it is apparent that due to the incomplete encapsulation of an isolation amplifier according to the prior art described above, the isolation of the high-voltage input side is weakened. In contrast, it is also apparent that by the transmission of signals representing the measurement signal and, if applicable, auxiliary parameters from the input-circuit side to the output-circuit page and, if applicable, electrical energy within the device via galvanically isolating coupling sections and an arrangement of input elements within an electrical circuit with close to earth potential, for example in the output circuit, no weakening of the high-voltage isolation results. It should be noted here that for the contact protection of a user it is particularly relevant that input elements within a circuit are at such a potential, in general a near-earth potential, which on contact does not cause dangerous shock currents, in other words at a low-voltage potential. A circuit suitable for the arrangement of input elements for an isolation amplifier according to FIG. 3, therefore, cannot only be the output circuit 2 but also the primary power supply circuit 41, provided that the primary power supply connector 44 only has suitable, in general near-earth potentials, in other words only low-voltage potential.